Progress Thread At the end of my tether!


New Member
Jan 24, 2020
Hi all, I've got a 65 mustang coupe. Everything stock (as far as I know) with stock 289, and I've installed the first bits of upgraded kit and I'm battling problems.

Ive fit an edelbrock rpm airgap intake manifold and 1406 performer 600cfm Carb. Since I've done this, I can't get the car to idle in gear. It just cuts straight out.

Ive searched and searched for vacuum leaks and can't find any. I've even removed and refit the intake with brand new gaskets for a second time to make sure I hadnt fluffed it on the first go.

The only vacuum ancillaries I have connected are the pcv and c4 transmission. I've even been underneath and replaced the vacuum modulator in the transmission and new flexi pipe to make sure it wasn't leaking from there.

Timing is set at 12degrees

Mixture screws are 1.5 turns out.

Ive checked the fuel system from the pump forward. Getting plenty of fuel in the Carb and the fuel filter looked clean.

Ive checked vacuum and its holding 20hg

Ive tried the Carb cleaner test all around all connecting faces and am still coming up dry.

Is it a case of setting a higher curb idle and just dealing with it?

Any help would be greatly appreciated, cheers.
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"Getting plenty of fuel in the Carb" I am no carb expert, but this is your clue...fuel, air, spark. Either you are getting too much fuel or not enough air(at idle at least). Since you indicated that this is an idle problem, I assume it runs fine otherwise so spark isn't the issue. It sounds like your idle mixture is rich from the description, what do your spark plugs look like after idling in neutral/park for a few minutes?(I can't even say its too much rather than not enough fuel...but regardless, the mixture is wrong...and short of a wideband, plug reading is the first step)
I read a discussion the other day on aftermarket intake manifolds on stock small block Fords. The conclusion was that the stock Ford 4 barrel manifold will out perform an aftermarket manifold on a stock SBF. I remember installing a Performer intake on a stock 302. It was a waste of money plus the intake manifold and head surfaces were not parallel.

You're only looking at part of the picture.

That engine is essentially stock, with only a camshaft upgrade. Look at the port size/flow difference between stock and all of the the aftermarket intakes (feel free to ignore the tunnel rams since we're talking street cars here).

Now, when you get down to the dyno results chart, THAT is where you're going to find the real gold.

The stock 4bbl intake from Ford (assuming either early, pre-EGR, or the mid 80s manifold with EGR) is a surprisingly good piece performance-wise, and for someone dealing with California emissions, the mid 80s aluminum 4-bbl manifold with EGR is 100% what I'd recommend all day. Even the old iron pig from the 60s and early 70s isn't horrible, especially when you look at low end torque, but it's heavy, and holds in more heat than an aluminum manifold. However, take a look at 3000rpm or so. Notice how the stocker starts losing it's low-end advantage to the Edelbrock Performer? Take a look at the other dual-plane intakes, the same trade-off happens in the same area, give or take a few hundred RPM.

If throwing a Performer on your 302 cost you power/drivability, it probably had a lot to do with the overall gearing. Tire size, rear gear ratio, and transmission ratios all have every bit to do with your acceleration and drivability. If you don't match everything from one end of the car to the other, the car won't perform well.

Take my Mustang II for example. It runs a set of heavily modified heads, a slightly rowdy camshaft, roller rockers, and a ported Performer RPM manifold. If it wasn't for the 3300rpm stall torque converter and the 4.11 rear gears, it'd fall on it's ass off the line, in spite of the fact that the engine makes fantastic power for an old iron-headed relic.

I put an Edelbrock Performer 289 manifold on a stock 302 years ago as well, luckily I was upgrading from 2bbl to 4bbl, so I had a significant improvement in power overall, but it was still a little sluggish off the line, possibly a little more so. Why? I killed the low-end torque and it had 2.79 rear gears and a stock converter in it's C4 transmission.

You've got to look at the whole package.